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Abstract:

The invention concerns a mold for forming a single-use floss holder
containing a length of dental floss having a wax composition applied
thereto, the mold including a first part having a first cavity disposed
therein, the first cavity defined by a bottom base surface and a
peripheral sidewall, and including a base portion, first and second
spaced-apart portions having proximal and distal sections and extending
from the base portion, and a second part having a second cavity disposed
therein, the second cavity defined by a bottom base surface and a
peripheral sidewall, and including a base portion, first and second
spaced-apart portions having proximal and distal sections and extending
from the base portion and terminating in the distal section; and a groove
having an aspect ratio of about 10:1 or greater and having first and
second terminal sections and a mid-section, the groove extending an
entire width of the second part, where the first and second terminal
sections of the groove traverse and are coincident with the distal
section of the first and second spaced-apart portions of the second
cavity, respectively.

Claims:

1. A mold for forming a single-use floss holder containing a length of
dental floss comprising a wax composition applied thereto, said mold
comprising: a first part comprising a first cavity disposed therein, said
first cavity defined by a bottom base surface and a peripheral sidewall,
said first cavity comprising, a base portion, and first and second
spaced-apart portions having proximal and distal sections, said lateral
portions extending from said base portion, a second part comprising a
second cavity disposed therein, said second cavity defined by a bottom
base surface and a peripheral sidewall, said second cavity comprising, a
base portion, and first and second spaced-apart portions having proximal
and distal sections, said later portions extending from said base portion
and terminating in said distal section; and a groove having first and
second terminal sections and a mid-section, said groove extending an
entire width of said second part, said first and second terminal sections
of said groove traversing and coincident with said distal section of said
first and second spaced-apart portions, respectively, said groove having
an aspect ratio of about 10:1 or greater.

2. The mold of claim 1, wherein said groove has an aspect ratio of
between about 10:1 and 100:1.

3. The mold of claim 1, wherein said groove has an aspect ratio between
about 25:1 and about 75:1.

4. The mold of claim 1 further comprising a heat sink disposed proximate
each of said first and second terminal sections of said groove coincident
with said distal section of said first and second spaced-apart portions.

5. The mold of claim 4, wherein said groove has an aspect ratio between
about 25:1 and about 75:1.

6. The mold of claim 4 wherein said heat sink is disposed within said
first part.

7. The mold of claim 4 wherein said heat sink is disposed within said
second part.

8. The mold of claim 1 wherein said terminal section of said groove has a
depth of about 0.002 inches.

9. The mold of claim 1 wherein said terminal section of said groove has a
width of about 0.100 inches.

10. The mold of claim 1 wherein the width of said mid-section of said
groove is greater than the width of said first and second terminal
sections of said groove.

11. The mold of claim 1 wherein said base portion of said first cavity is
substantially horizontal and comprises first and second terminal
sections, and said first and second spaced-apart portions of said first
cavity are substantially lateral, are substantially transverse to said
base portion of said first cavity and extend from said first and second
terminal sections of said base portion of said first cavity,
respectively; and said base portion of said second cavity is
substantially horizontal and comprises first and second terminal
sections, and said first and second spaced-apart portions of said second
cavity are substantially lateral, are substantially transverse to said
base portion of said second cavity and extend from said first and second
terminal sections of said base portion of said second cavity,
respectively.

Description:

FIELD OF THE INVENTION

[0001] This invention relates to an apparatus used to manufacture
single-use floss holders that contain wax coated dental floss.

BACKGROUND OF THE INVENTION

[0002] A number of single-use flossing devices are know and commercially
available. Such devices typically have a floss holder that includes two
spaced-apart arms extending upwardly, or outwardly, from a base to form a
generally U-shaped configuration with the floss attached at each end to
one of the arms and spanning the distance between the spaced-apart arms.
The devices also include a handle portion in association with the floss
holder.

[0003] In some devices, the dental floss holder itself is removable from
the handle portion and thus replaceable. Such devices generally include a
handle with a head portion designed to receive and hold the dental floss
holder. In use, the dental floss holder is attached to the head portion
of the handle and the floss is inserted between teeth. After flossing,
the dental floss holder is removed from the head of the handle and
replaced with a new dental holder. Such devices are shown in, for
example, U.S. Pat. Nos. 5,483,982, 7,059,334, 7,174,904 and 7,325,554,
the content each of which is hereby incorporated by reference in its
entirety. It is noted that devices exemplified in such patents and
commercial products made according to the disclosures of such patents do
not use wax coated yarns. In other devices, the dental floss holder is
integral with the handle portion to form a unitary device, such that the
entire device may be disposed of after completion of flossing.

[0004] In one method of manufacturing such devices and attaching the floss
to the arms of the floss holders, the floss holder, whether removable
from or integral with the handle, typically is molded from plastic around
the uncoated floss to provide the generally U-shaped floss holder having
the floss attached to and extending between the spaced-apart arms of the
holder. As noted, holders may be molded integral with a handle portion to
form a unitary device, or may be molded with means to rigidly connect the
detachable floss holder to the head of a handle which is configured to
receive the detachable floss holder.

[0005] Flosses in general must be capable of passing between several teeth
without significant fraying or breaking during insertion of the floss
between the teeth and also during the up and down motion of the flossing
process. For this reason, some yarns are made from an extremely strong
material, such as ultra high molecular weight polyethylene (UHMWPE).
Furthermore, multifilament yarns that are highly twisted, i.e. having
more than two turns per inch, to hold adjacent fibers, or filaments,
tightly together during the flossing process also are used. Twists of 3
or 4 twists per inch are typical. Makers of traditional floss sold in
conventional dispensers have found consumers prefer softer flosses that
slide more easily between teeth and are gentler on gums. For this reason,
manufactures have reduced or eliminated twist in such multifilament
yarns. However, this typically results in an increase in fraying and
breaking. In order to maintain reduced fraying and breaking, manufactures
have impregnated the space between fibers with soft polymers such as
microcrystalline wax or beeswax.

[0006] While coated multifilament yarns are suitable for use when
dispensed from a conventional floss dispenser, where the floss is wrapped
around a spool, wax coated multifilament flosses are not known to be used
in commercial single-use floss devices as described above. This is due,
in part, to difficulties associated with the manufacture of such devices
using wax coated multifilament yarns.

[0007] In summary, there is a need for a single-use flossing device that
uses flosses that slide more easily between teeth and are gentler on
gums, while maintaining strength to reduce fraying and breakage, as well
as methods and apparatus for making such single-use devices. As described
below, it now has been discovered how to provide single-use flossing
devices using wax coated dental floss.

SUMMARY OF THE INVENTION

[0008] The invention concerns a mold for forming a single-use floss holder
containing a length of dental floss having a wax composition applied
thereto, the mold including a first part having a first cavity disposed
therein, the first cavity defined by a bottom base surface and a
peripheral sidewall, and including a base portion, first and second
spaced-apart portions having proximal and distal sections and extending
from the base portion, and a second part having a second cavity disposed
therein, the second cavity defined by a bottom base surface and a
peripheral sidewall, and including a base portion, first and second
spaced-apart portions having proximal and distal sections and extending
from the base portion and terminating in the distal section; and a groove
having an aspect ratio of about 10:1 or greater and having first and
second terminal sections and a mid-section, the groove extending an
entire width of the second part, where the first and second terminal
sections of the groove traverse and are coincident with the distal
section of the first and second spaced-apart portions of the second
cavity, respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a perspective view of a conventional mold used to prepare
conventional single-use floss holders.

[0010] FIG. 1a is a cross-sectional view of the groove depicted in FIG. 1.

[0011] FIG. 1b is a top plan view of the distal sections of the lateral
cavities in the second mold part as depicted in FIG. 1, with projections
of the first part shown in phantom as they would be positioned when first
and second mold parts are brought together.

[0012]FIG. 2 is a perspective view of a mold according to the present
invention.

[0013] FIG. 2a is a cross-sectional view of the groove depicted in FIG. 2.

[0014] FIG. 2b is a top plan view of the distal sections of the lateral
cavities in the second mold part as depicted in FIG. 2, with projections
of the first part shown in phantom as they would be positioned when first
and second mold parts are brought together.

DETAILED DESCRIPTION OF THE INVENTION

[0015] In attempting to use conventional molds that are used for making
conventional single-use floss holders that use floss that does not
include a wax coating, problems were discovered that prevented the use of
such molds to make floss holders that utilize wax coated floss. It was
found that wax from the coated dental floss builds up in the groove of
the conventional mold where the length of floss is held between the two
mold halves at the time of molding the floss holder about the floss. The
degree of buildup in the groove is dependent upon not only the amount of
wax on the floss, but also on the amount of wax actually in contact with
the mold surface. It was discovered that, as the groove filled with
residual wax from the dental floss, there was less and less room for the
floss to nest within the groove in the mold so that the floss holder may
be molded around the floss. Eventually, wax was deposited in the groove
of the conventional mold to an excessive level, which contributed to
floss breakage, thus causing the molding operation to stop. With the
level of wax used on conventional waxed flosses, it was found that
buildup and breakage using conventional molds typically occurred after
about 5 to 10 molding cycles, thus making commercial manufacture of such
floss holders with conventional molds cost prohibitive.

[0016] In addition to the contribution to floss breakage caused by wax
buildup, other factors limiting commercial feasibility of single-use
flossing devices using wax coated yarns exist. One issue is the melting
problem encountered during the insert molding operation. Typically,
conventional single-use flossing heads, or floss holders, are made from
polypropylene that has a melt temperature around 160° C. The floss
around which the floss holders are molded is made from ultra high
molecular weight polyethylene (UHMWPE) having a melt temperature around
125° C. Extrusion barrel temperatures of 180° C. to
190° C. are typical and insertion nozzle temperatures of up to
325° C. are used to inject the resin for forming the floss holder
into the mold. This means that hot molten resin is pumped into a mold and
contacts the floss that has a much lower melt temperature. As such, heat
may be transferred to the floss at levels sufficient to melt the floss.

[0017] In the case of highly twisted UHMWPE floss that does not contain a
wax coating, the molten resin used to form the floss holder does not
penetrate the floss due to the twist and tightness of the floss and thus
there is an insufficient amount of heat transferred to melt the floss.
However, in the case of wax coated UHMWPE floss, it is believed that the
wax acts as a heat transfer agent between the molten resin and the UHMWPE
and partial or complete melting of the floss may occur where the resin
contacts the floss.

[0018] The present invention provides a solution to these significant
problems associated with conventional molds and methods used when
attempting to make single-use floss holders that utilize dental floss
that has a wax coating composition applied thereto. Molds according to
the present invention useful for forming single-use floss holders
containing a length of dental floss that has a wax composition applied
thereto solve problems associated with heat transfer attributable to the
wax composition and/or excessive wax buildup in the floss groove of the
mold. As used herein, dental floss, or floss, include various forms of
dental floss, including multifilament yarns, whether twisted or
untwisted, monofilament dental tape, e.g. core sheath dental tapes, and
monofilament elastomeric dental tape formed by extrusion of the
elastomeric material.

[0019] Molds according to the present invention may be made from hardened
tool steel, although aluminum may also be used. The molds include a first
part and a second part, which also may be considered as top and bottom
parts, which are brought together during formation of the dental floss
holder of the present invention. The first part comprises a first cavity
defined by a bottom base surface and a peripheral wall. The first cavity
includes a base portion and first and second spaced-apart portions having
proximal and distal sections extending from the base portion. Each
spaced-apart portion terminates in the distal section thereof. The first
cavity may be generally V-shaped or U-shaped, for example. The base
portion may be substantially horizontal and comprise a mid-section and
first and second terminal sections, as shown herein below. In certain
embodiments, the first and second spaded-apart portions are substantially
lateral and disposed substantially transverse to the substantially
horizontal base portion. In this embodiment, the lateral spaced-apart
portions extend from the first and second terminal sections,
respectively, of the base portion to form the generally U-shaped cavity.

[0020] The second part comprises a second cavity disposed therein,
substantially corresponding in both shape and size to the first cavity in
the first part. The second cavity in the second part is defined by a
bottom base surface and a peripheral sidewall. The second cavity includes
a base portion and first and second spaced-apart portions having proximal
and distal sections extending from the base portion. Each spaced-apart
portion terminates in the distal section thereof. In certain embodiments,
the first and second spaded-apart portions are substantially lateral and
disposed substantially transverse to the substantially horizontal base
portion. In this embodiment, the lateral spaced-apart portions extend
from the first and second terminal sections, respectively of the base
portion to form the generally U-shaped cavity.

[0021] Molds used to form floss holders of the present invention utilize
grooves specifically designed to prevent buildup of the wax coating
within the groove, thus minimizing or alleviating the problems associated
with wax buildup. The groove comprises first and second terminal sections
and a mid-section. The groove may be located in either the first or the
second part, although as shown and discussed herein it is disposed in the
second, or bottom, part. The groove extends the entire width of the
second mold part, with the first and second terminal sections of the
groove traversing, or spanning, and being coincident with the distal
section of the first and second spaced-apart portions, respectively.

[0022] Floss grooves in molds according to the present invention have an
aspect ratio (width:depth) of about 10:1 or greater, or between about
10:1 to about 100:1, or between about 25:1 to about 75:1, or about 50:1.
The mid-section of the groove may be wider and/or deeper than the
respective terminal sections to reduce contact with the length of wax
coated dental floss during molding of the floss holders of the present
invention. For example, the mid-section may be from about from about 2 to
about 10 times deeper and/or from about 1.2 to about 1.5 times wider than
the terminal sections. A groove for a typical 400 denier yarn would be
about 0.010 inch radius groove cut of about 0.02 inch deep and about
0.020 inch wide. Conventional molds for forming conventional single-use
flossing devices using uncoated floss utilize grooves typically having an
aspect ratio (width:depth) between about 1:1 and about 4:1. The
cross-sectional configuration of the groove may vary from a semi-circle
to almost V-shaped to easily capture and compact a length of floss
between the mold halves. The conventional groove also may have a
mid-section and terminal sections, where the mid-section may be wider
than the terminal sections. The cross-sectional area of the groove is
essentially the same cross-sectional area of the floss.

[0023] While the aspect ratios and cross-sectional configuration of
grooves of conventional molds and grooves of molds according to the
present invention are vastly different, the overall volume of the grooves
is approximately equal. The cross-sectional configuration of grooves used
in molds according to the present invention is substantially rectangular
and has a substantially flat bottom surface, as compared to
cross-sectional configurations of grooves in conventional molds. This
prevents or minimizes buildup of wax in the groove, while at the same
time providing for greater tolerance in placement of the length of floss
within the groove of the mold, thus allowing for some lateral
misalignment of the floss in the groove. As such, problems associated
with conventional molds relating both to breakage and misalignment of
floss are synergistically improved.

[0024] In embodiments where the wax composition may serve as a heat
transfer agent, the mold may further include one or multiple heat sink
disposed proximate each of the first and second terminal sections of the
groove that is coincident with the distal section of the first and second
lateral spaced-apart portions, respectively. As used herein, "heat sink"
means an object that absorbs and dissipates heat from another object,
e.g. the length of coated dental floss, using thermal contact, which
contact may be either direct or radiant. As used herein, "proximate each
of the first and second terminal sections" means that the heat sink is
disposed either in contact with the terminal section of the groove, or at
a distance sufficiently close to the terminal section of the groove, such
that it is effective to transfer heat away from the length of dental
floss to the heat sink, thereby reducing breakage in the floss due to
melting during molding of the floss holder about the floss. During
molding of the floss holder, the heat sink is proximate the terminal ends
of the length of dental floss disposed in the distal portions of the
spaced-apart portions of the cavity. As with the groove, the heat sink is
in contact with, the length of dental floss, or at a distance
sufficiently close to the length of dental floss, such that it is
effective to transfer heat away from the length of dental floss. The heat
sink may shield one side or both sides of the floss from the molten resin
forming the floss holder, as well as direct the flow of resin around the
floss.

[0025] One embodiment of a heat sink according to the invention is shown
in FIG. 2. As shown therein, a projection is disposed in the first cavity
of the first part. The projection serves, on the one hand, to form a
cavity in the final floss holder for holding, e.g. a flavor composition.
In addition, the projection is located in the first cavity of the first
part such that it is proximate the terminal sections of the groove in the
second part when the two parts of the molds are brought together. As a
result, the heat sink is proximate the length of coated dental floss
during molding of the dental floss holder and serves as a heat sink.
While the conventional mold shown in FIG. 1 also includes the projection
disposed in the first cavity to form a cavity in the floss holder for
holding, e.g. a flavor composition, when the mold parts are brought
together, the projection is not proximate the groove. As a result, the
length of floss held in the conventional mold is not proximate the
projection during molding and the projection does not serve as a heat
sink. In embodiments of the invention requiring a heat sink, the relative
location of the projection and groove in the mold then are critical in
assuring that the projection will serve as a heat sink during formation
of the floss holder. While FIG. 2 shows the projection in a position that
will serve as a heat sink, in those embodiments of the invention that do
not require a heat sink, the projection need not be proximate the
terminal sections of the groove.

[0026] Alternatively, a pressure release pin could function as a heat sink
in the mold. In this case, the pin is proximate the terminal sections of
the groove and contacts, or shields, one side of the wax coated floss
until the final pressure is reached inside the mold, at which point the
pressure forces the pin to recede into the body of the mold, thereby
closing the cavity area. As with the molds themselves, the heat sink may
be made from hardened tool steel, although aluminum may also be used.

[0027] Floss holders produced utilizing molds according to the present
invention may be made integral with a handle, such as unitary single-use
disposable flossing devices, which may then be disposed of after use.
Alternatively, floss holders produced according to the present invention
may be made with a fitment to allow the floss holder to be rigidly, but
removably, attached to a separate handle. The floss holder itself then
would be disposable and the handle re-usable.

[0028] In one embodiment, the floss holder is generally U-shaped and
includes a substantially horizontal base portion having a mid-section and
first and second terminal sections. First and second substantially
lateral spaced-apart arms are integral with and substantially transverse
to the base portion. The lateral arms each have a proximal end integral
with the first and second terminal sections of the base portion,
respectively. Each lateral arm terminates in a distal section thereof.
The arms extend from the first and second terminal sections of the base
portion, respectively, thus forming the generally U-shaped configuration.
A length of floss having a wax composition applied thereto extends
between the spaced-apart arms and is rigidly attached at each end of the
floss in the distal section of each of the spaced-apart arms. The floss
may be anchored in the spaced-apart arms by the use of knots formed on
the outside of the respective arms, formed by heating the floss above the
melting point, thus forming beads of melted floss on the outside surfaces
of the respective spaced-apart arms. The holder can be made from a
polymer such as polypropylene, polystyrene, polyethylene or other similar
molding materials.

[0029] The length of floss that extends between the lateral spaced-apart
arms may be a made from a multifilament yarn, or a monofilament floss, or
tape. Because of the need to pass between multiple teeth, the floss needs
to be very fray resistant. For this reason, the preferred material of the
multifilament yarn is Ultra High Molecular Weight Polyethylene (UHMWPE)
with a denier of about 400 and a filament size of approximately 1 dpf.
Filaments larger than 1 dpf will also work, but more coarse filaments
result in increased insertion force between teeth and are less desirable.
Filaments below 1 dpf filament would also be useable although, no
manufacturer currently makes such a filament. Yarns of this nature are
supplied under the trade name DYNEEMA by companies such as DSM (DSM
Dyneema B.V., Urmond, the Netherlands), and designated as SK65. Other
materials could be used, but the high strength and fine filament of the
UHMWPE make it the most desirable of materials.

[0030] The uncoated multifilament yarns used on known single-use flossing
devices are highly twisted, e.g. more than two turns per inch, to hold
adjacent fibers tightly together during the flossing process, thus
preventing fraying. Twists of 3 or 4 twists per inch are typical. In the
present invention, high twisted or low twist yarn may be used. Low
twisted yard in herein defined as being twisted less than 2 twists per
inch of yarn, and ideally should be twisted about 1.5 twists per inch.
This provides a good balance between soft feel, fray resistance and
insertion force. No twist yarn with air entangled nodes also may be used
in the current invention.

[0031] In addition to multifilament yarns, flosses manufactured using
molds according to the present invention may be made from monofilament
tape, such as are disclosed in US2009/0120454 A1, the contents of which
is hereby incorporated by reference in its entirety. Such monofilament
dental tapes include a core body having an aspect ratio of greater than
about 5:1 and a first cleaning surface and a second cleaning surface
opposite the first cleaning surface, where at least one of the first and
second cleaning surfaces includes a plurality of ribs disposed along the
length thereof, and where the ratio of the width of the dental tape to
the thickness of the dental tape is from about 3:1 to about 25:1.

[0032] Elastomeric materials that may be used to form such dental tape
include, but are not limited to, polyamide-polyether block copolymers
sold under the tradename PEBAX (Ato Chimie, Hauts-de-Seine France), such
as PEBAX 7033, 5533 MX1205, 4033, 3533, and 2533; polyester-polyether
block copolymers and polyester-polyester block copolymers sold under the
tradename HYTREL (E. I. du Pont de Nemours & Co., Wilmington, Del.), such
as HYTREL 7246, 5556, and 4056; aliphatic thermoplastic polyurethane
elastomers sold under the tradename TECOFLEX (Lubrizol Advanced
Materials, Inc., Cleveland Ohio); aromatic thermoplastic polyurethane
elastomers sold under the tradename PELLETHANE (Dow Chemical Co.,
Midland, Mich.); and thermoplastic polyolefin elastomer sold under the
name MULTI-FLEX (Dow Chemical Co., Midland, Mich.). Non-elastomeric
materials from which the dental tape can be made include nylon or
polytetrafluoroethylene (PTFE).

[0033] The length of dental floss used in the single-use floss holders of
the present invention has a wax composition applied thereto to slide more
easily between teeth and to be gentler on the gums. In addition to better
sliding between teeth, the wax composition also serves to bind the
filaments of a low twist yarn together, thus preventing fraying. The
dental floss may contain about 10 percent or more, for example about 25
percent or more, of the wax composition applied thereto, based on weight
of the length of dental floss. In certain embodiments, the length of
dental floss may contain from about 25 percent to about 50 percent of the
wax composition applied thereto, based on the weight of the length of
dental floss.

[0034] The coating on the floss comprises waxes and may include further
additives. Additives to the wax composition are used to prevent transfer
of coatings to the molds and for better adhesion of the wax composition
to the plastic comprising the molded head, i.e. floss holder. An
exemplary wax useful in the wax compositions for the floss is Multiwax
W-445, made by the Petroleum Specialties Group of Witco Corp. (New York,
N.Y.), although other grades of microcrystalline wax (MCW) having melting
points from about 76° C. to about 85° C. and a hardness of
about 14 to about 25 dm would suffice. In addition or alternatively,
beeswax, such as Strahl and Pitsch white beeswax NF-SP422 and similar
waxes, may be used. In some embodiments, the wax composition comprises
from about 10 percent to about 95 percent by weight of microcrystalline
wax, based on total weight of the wax composition. Additives to the wax
composition include items that make the wax less sticky and/or increase
the floss adhesion within the head, while not appreciably decreasing the
pliability of the bundle of fibers. This allows the floss to move freely
with minimal separation of individual fibers from the bundle during the
rigors of flossing. One such additive is an ethylene vinyl acetate
copolymer, such as A-C 400 grade manufactured by Honeywell (Honeywell
International, Morristown, N.J.). Other additives also may be used, such
as polyethylene homopolymers from Honeywell, e.g. A-C 617. Polymers
useful as additives will exhibit a combination of compatibility with the
wax, the appropriate melt temperature, a low viscosity and the
appropriate hardness. The polymers having a melt temperature between
about 80° C. and 120° C., a viscosity below about 600 cps
and a hardness (ASTM D-5) between about 1 and about 9, appear to be
advantageous.

[0035] While the flossing device can be made successfully without any
additive, it may be desirable to use an additive to increase the adhesion
of the floss within the floss holder. For example, the wax composition
may include from about 5 percent to about 40 percent by weight of the
additive, or about 20 percent by weight, based on total weight of the
composition. While other ranges may work, about 20 percent provides a
good balance between pliability, softness, slideability, adhesion within
the floss holder and minimum wax buildup within the molding operation.

[0036] In processes for making a single-use dental floss holder according
to the present invention, which comprise a length of dental floss having
a wax composition applied thereto, a length of dental floss having a wax
composition applied thereto is provided. Uncoated yarn or dental tape,
either multifilament or monofilament, is supplied in rolls typically
weighing approximately 1 to 5 kilograms. Multifilament yarn may have a
twist, no twist, or be air entangled, each utilizing known commercial
technologies.

[0037] The supply rolls holding the uncoated dental floss are passed
through standard floss coating equipment, where wax coatings are applied,
and the coated floss is rewound onto supply rolls for further processing.
One skilled in the art will recognize that any wax coating process and
coating equipment conventionally used to prepare conventional wax coated
dental floss may be employed. The temperature of the wax coating
composition and the application die used in the coating process is
dependent upon the coating being applied. Typically for microcrystalline
wax coatings, it is desirable to apply the coating at temperatures
significantly higher than the melting point of the wax in order to
achieve good penetration of the wax into the inner fibers of the yarn, in
the case of the multifilament yarn. This is typically 90° C. to
95° C. for Witco W-445. For a mixture of about 80 percent
microcrystalline wax and about 20 percent EVA, this temperature is
typically about 95° C. to about 115° C. Distributing the
wax into the inside of the multifilament yarn bundle provides enhanced
binding of internal fibers and also minimizes wax on the surface of the
floss, which can contribute to wax buildup in the groove of the mold used
to form the floss holder, thus contributing to floss breakage during
insert molding.

[0038] The supply roll holding the wax coated floss is then provided to an
insert molding machine that includes a mold having a cavity for receiving
molten plastic material and a groove for receiving a length of the wax
coated dental floss in one half of the mold. The groove in the mold has
an aspect ratio of about 10:1 or greater. The floss is pulled through the
two open mold halves and positioned in the groove of the mold such that
the terminal ends of the length of dental floss span the respective
distal sections of the cavity in the mold half containing the groove. The
mold optionally may include a heat sink or heat sinks proximate the
groove and length of wax coated dental floss. The mold halves are then
brought together and the molten plastic is then injected via an injection
nozzle into the cavity of the mold, thus forming flossing heads, or floss
holders, around the terminal ends of the floss.

[0039] The temperature of the resin entering the mold affects the
retention force of the floss within the head. An optimum temperature of
the resin is one in which no melting of the floss occurs. A temperature
higher than optimum results in lower retention force, as part of the
floss within the head is melted during the molding process, thus reducing
the retention force. The temperature of the resin entering the mold is
affected by the four controllable temperature points within the extrusion
barrel, the nozzle temperature and the hot manifold temperature. These
temperatures are selected such that the force required to pull the floss
from the ends of the finished floss holder is about four pounds or
greater, e.g. about 5 pounds or greater. If the temperature of the resin
is too high, the force required to pull the wax coated dental floss from
the respective lateral portions of the floss holders will not be
sufficiently high. The actual temperature selected will depend on factors
such as the particular dental floss, the concentration of wax coating
applied to the dental floss, the composition of the wax coating and the
presence, or not, of a heat sink located proximate the groove of the mold
and the length of dental floss positioned within the mold. In certain
embodiments, the temperature of the injection nozzle will be about
300° C. or less, or about 275° C. or less, or from about
210° C. to about 290° C., or from about 220° C. to
about 270° C. It has been discovered that by using a heat sink, as
described herein, in combination with a groove having an aspect ratio of
about 10:1 or greater, the variation in the pull out force can be
reduced, while also improving the minimum pull out force expected to pull
the floss from the floss holder.

[0040] The molded floss holders are typically attached to a cold runner
for cooling and to at least to strands of floss which are used to
extricate the molded parts from the mold once the parts have solidified
upon cooling and after the mold is opened. Each attached group of floss
holders is then separated from the next group by cutting the floss
between the respective groups. An open flame is used to cut the floss
between adjacent holders. This burning process melts and shrinks the
excess floss back to the exterior of the lateral arm of the floss holder,
thus forming a knot in the terminal section of the floss at exterior side
of the distal section of the lateral arm, which holds the floss in place.

[0041] As mentioned earlier, an issue with making single-use flossing
heads, e.g. floss holders, having wax coated floss is the problem of
molding molten materials, e.g. plastics, around the wax coated floss. One
the one hand, wax from the floss builds up in the groove of the mold
where floss is held between the mold halves. One the other hand, the wax
may serve as a heat transfer agent, contributing to melting of the floss
during the molding operation. The molds of the present invention overcome
this problem.

[0042] FIG. 1 is a perspective view of a prior art mold used to
manufacture conventional single-use floss holders utilizing dental
flosses that do not contain a wax coating. Mold 50 has first part 40 and
second part 10. First part 40 is a rectangular prism, with top face 42,
bottom face 44, and side faces 46, 48, 52, and 54. First part 40 further
includes generally U-shaped first cavity 56 disposed therein. Cavity 56
is defined by peripheral sidewall 56d and cavity bottom surface 56e, with
sidewall 56d extending between the plane of cavity bottom surface 56e and
the plane of bottom face 44. Cavity 56 includes horizontal base cavity
portion 56a, having first 56k and second 56l terminal sections, and
substantially lateral spaced-apart cavity portions 56b and 56c, each
having proximal sections 56f, 56g and distal sections 56h, 56i,
substantially transverse to and extending in the same direction away from
the first 56k and second 56l terminal sections of base cavity portion
56a, to form the generally U-shaped configuration. Projections 58b and
58c are disposed within lateral cavity portions 56b and 56c,
respectively, for forming a cavity in the floss holder for containing,
for example, compositions containing flavors.

[0043] Second part 10 has top face 12, bottom face 14, and side faces 16,
18, 22, and 24. Second part 10 is a rectangular prism, and has generally
U-shaped second cavity 32 disposed therein. Cavity 32 is defined by
peripheral sidewall 32d and cavity bottom surface 32e, with sidewall 32d
extending between the plane of cavity bottom surface 32e and the plane of
top face 12. Cavity 32 includes base cavity portion 32a, having first 32f
and second 32g terminal sections, and substantially lateral spaced-apart
cavity portions 32b and 32c, each having proximal sections 32h, 32i and
distal sections 32j, 32k, substantially transverse to and extending in
the same direction away from first 32f and second 32g terminal sections
of base cavity portion 32a, to form the generally U-shaped configuration.

[0044] Floss groove 34 is situated transverse of lateral cavity portions
32b and 32c, with the location of groove 34 corresponding to the desired
location of where the length of floss spans cavity portions 32b and 32c.
Groove 34 has mid-section 34c and terminal sections 34b and 34a.
Injection port 36 is located within rear side faces 18 and 48 of first
part 40 and second part 10, respectively. During the injection molding
process, molten resin passes through injection port 36 and fills the mold
cavity formed by first cavity 56 and second cavity 32 when first 40 and
second 10 mold parts are brought together, thus embedding the length of
floss in the floss holder.

[0045] FIG. 1a is a cross-sectional side view of a terminal section of
groove 34. As shown, groove 34 has a substantially V-shaped or
semi-circular cross-sectional configuration. The bottom 34d of groove 34
forms a trough-like configuration in which the length of dental floss is
positioned during manufacture of the conventional dental floss holder.

[0046] FIG. 1b is a top plan view of distal sections 32j and 32k of
lateral cavities 32b and 32c, respectively, as depicted in FIG. 1.
Terminal sections 34a and 34b of groove 34 traverse, or span, distal
sections 32j and 32k of lateral cavities 32b and 32c, respectively.
Projections 58b and 58c of the first part are shown as they would be
positioned within lateral cavities 32b and 32c, respectively, when the
two halves of the mold are brought together. As shown, projections 58b
and 58c are not proximate terminal sections 34a or 34b of groove 34.
Consequently, projections 58b and 58c do not function as a heat sink in
the prior art mold.

[0047]FIG. 2 is a perspective view of a mold according to the present
invention. Mold 70 has first part 90 and second part 80. Mold 70 may be
made from hardened tool steel, although aluminum may also be used. First
part 90 is a rectangular prism, with top face 92, bottom face 94, and
side faces 95, 96, 97, and 98. First part 70 further includes generally
U-shaped first cavity 100 disposed therein. Cavity 100 is defined by
peripheral sidewall 100d and cavity bottom surface 100e, with sidewall
100d extending between the plane of cavity bottom surface 100e and the
plane of bottom face 94. Cavity 100 includes base cavity portion 100a,
having first 100f and second 100g terminal sections, and substantially
lateral spaced-apart cavity portions 100b and 100c, each having proximal
sections 100h, 100i and distal sections 100j, 100k, substantially
transverse to and extending in the same direction away from the first and
second terminal sections of base cavity portion 100a, to form the
generally U-shaped configuration. Projections 102b and 102c are disposed
within lateral cavity portions 100b and 100c, respectively, for forming a
cavity in the floss holder for containing, for example, compositions
containing flavors.

[0048] Second part 80 has top face 82, bottom face 84, and side faces 85,
86, 87 and 88. Second part 80 is a rectangular prism and has generally
U-shaped cavity 110 disposed therein. Cavity 110 is defined by peripheral
sidewall 110d and cavity bottom surface 110e, with sidewall 100d
extending between the plane of cavity bottom surface 110e and the plane
of bottom face 84. Cavity 110 includes base cavity portion 110a, having
first 110f and second 110g terminal sections, and substantially lateral
spaced-apart cavity portions 110b and 110c, each having proximal sections
110h, 110i and distal sections 110j, 110k, substantially transverse to
and extending in the same direction away from the first 110f and second
110g terminal sections of base cavity portion 110a, to form the generally
U-shaped configuration.

[0049] Floss groove 114 is situated transverse of lateral cavity portions
110a and 110b, with the location of groove 114 corresponding to the
desired location of where the length of floss spans cavity portions 110a
and 110b. The location of groove 114 is such that it is proximate
projections 102b and 102c during molding of the floss holder. In this
embodiment, given the proximate location of projections and floss groove,
the projections serve as a heat sink to dissipate heat away from the
length of floss during molding. In floss holders made utilizing such
molds, the length of coated floss is proximate the cavity of the floss
holder formed by projections 102b and 102c. Injection port 116 is located
within rear side faces 98 and 86 of first part 90 and second part 80,
respectively. During the injection molding process, molten resin passes
through injection port 116 and fills the mold cavity formed by first
cavity 100 and second cavity 110 when mold parts 90 and 80 are brought
together, thus embedding the length of floss in the floss holder such
that at least a portion of the length of floss is proximate the cavity
formed in the floss holder. Although shown as a single-part mold,
multiple-part molds having the capacity to form on the order of 20 or
more individual floss holders may be used in the manufacture of such
floss holders.

[0050] FIG. 2a is cross-sectional side view of groove 114. As shown,
groove 114 has a substantially rectangular cross-sectional configuration
having a substantially flat bottom surface 114d in which the length of
dental floss is positioned during manufacture of the dental floss holder
of the present invention.

[0051] FIG. 2b is a top plan view of distal sections 110j and 110k of
lateral cavities 110b and 110c, respectively, as depicted in FIG. 2.
Terminal sections 114a and 114b of groove 114 traverse, or span, distal
sections 110j and 110k of lateral cavities 110b and 110c, respectively.
Projections 102b and 102c of the first part are shown as they would be
positioned within lateral cavities 110b and 110c, respectively, when the
two halves of the mold are brought together. As shown, projections 102b
and 102c are proximate terminal sections 114a or 114b of groove 114.
Consequently, projections 102b and 102c function as a heat sink in the
mold during manufacture of dental floss holders according to the present
invention.

[0052] The pull out force is defined as the amount of force it would take
to pull the floss from a flossing head, i.e. a floss holder, or the
amount of force a user would have to apply to a flossing head to loosen
the floss such that the holder is inoperable. The minimum pull out force
of the floss preferably is above four pounds and more preferably above
five pounds. The technique to measure the force of removal is typically
accomplished by attaching the floss holder to an Instron or similar
device. A hook attached to the moveable side of the Instron is placed in
the middle of the floss holder. The hook is then slowly moved up, thus
hooking the mid-section of the floss in the process. The hook moves up at
a constant speed of approximately 10 inches per minute applying an
increasing force until it ultimately results in one side of the floss
pulling through the U-shaped head. This simulates the force the user
would have to exert on the floss in order for the flossing device to
become inoperative.

[0053] Examples are provided below to further illustrate the advantages of
the present invention. The invention should not be construed as being
limited to the specific detail set forth herein.

Example 1

[0054] A mold having a first, i.e. top, part and a second, i.e. bottom,
part was created, each part containing eight cavities for producing
single-use floss holders, 4 cavities on each side, with a cold runner
connecting the cavities. In one section of the top part of the mold, the
first part was similar to that shown in FIG. 2, where a projection was
located such that it served as a heat sink and formed a cavity in the
final floss holder. In the other section of the first part, no projection
was used and thus there was no cavity in the final floss holder. The
second part of the mold included grooves machined into the facing thereof
for receiving the length of floss when the mold halves were closed. Two
different configuration floss grooves similar to those shown in FIGS. 1
and 2 were used for comparison. A conventional groove (designated Groove
A below) having a cross-sectional semi-circle configuration with
approximately a 0.010-inch radius was machined into the mold half such
that the width at the facing of the mold was 0.020-inch and the depth
from the facing to the bottom of the groove was 0.010-inch, thus
providing an aspect ratio (w/d) of 2:1. The other groove used according
to the present invention (designated Groove B below) had a substantially
rectangular cross-sectional configuration and was 0.100 inch wide and
0.002-inch deep, thus providing an aspect ratio (w/d) of 50:1.

[0055] A number of flosses, both with and without wax coating applied
thereto, were tried on both sides of the mold to compare performance of
Groove A to Groove B. The molding conditions were as follows:

[0056] Insert Pressure 500 lbs

[0057] Hold Pressure 100 lbs

[0058] Barrel and manifold temperatures 182° C.

[0059] Insert Nozzle Temperature 315° C.

[0060] Cycle time 11.4 seconds

[0061] In the first set of trials, prototype single-use floss holders were
formed using a 400 denier UHMWPE multifilament floss having a variety of
coatings applied thereto. The results of the molding trials are
summarized in Table 1.

TABLE-US-00001
TABLE 1
Trial Floss Results of Molding Trials
1 400 denier UHMWPE, Ran well with Groove A
3 twists, no wax coating Ran well with Groove B
2 400 denier UHMWPE Created wax buildup in Groove A
with 1.5 twists with requiring cleaning after
25% wax coating approximately 50 cycles
(MCW (60%), PE 617 No perceivable buildup in Groove B.
(40%))
3 Same as 2 except Created wax buildup in Groove A
coating was 80% MCW No perceivable buildup in Groove B
and 20% PE
4 Same as 2 except Created wax buildup in Groove A
coating was 60% MCW No perceivable buildup in Groove B
and 40% EVA
5 Same as 2 except Created wax buildup in Groove A
coating is 80% MCW No perceivable buildup in Groove B
and 20% EVA
6 Same as 2 except Created wax buildup in Groove A
coating is 90% MCW No perceivable buildup in Groove B
and 10% EVA
NOTES:
MCW is microcrystalline wax, PE is polyethylene homopolymer, and EVA is
Ethylene Vinyl Acetate Copolymer.

[0062] Table 1 shows that UHMWPE floss containing no wax coating resulted
in no processing issues for either groove configuration. When single-use
floss holders were formed with wax-coated UHMWPE, however, wax coating
buildup occurred in the comparative Groove A, whereas little to no
coating buildup occurred in the inventive Groove B.

[0063] Next, a short manufacturing run was performed using only the
prototype mold side including Groove B to make single-use flossing
devices using a 400-denier SK-65 UHMWPE multifilament floss with 1.5
twists and having a 49 percent coating weight of a wax coating
composition comprising 60 percent MCW and 40 percent PE-617. This run was
to test the durability of the process. After 1.5 hours of run time, the
mold was opened and examined for buildup and debris. While a small amount
of buildup was seen, it was not sufficient to result in process stoppage
or to negatively impact the molding process.

Example 2

[0064] Molds used in Example 1 with Groove B (50:1 aspect ratio) were used
to prepare single-use dental floss holders utilizing two different
flosses. The first was a highly twisted multifilament floss yarn. This
floss was an unwaxed UHMWPE DSM SK 65 yarn with 3 twists per inch. The
second floss was UHMWPE DSM SK-65 yarn, 400 denier with 1.5 twists per
inch, and included 25 percent by weight of a coating containing 80
percent microcrystalline wax and 20 percent Honeywell EVA PE400. The
production conditions were as follows:

[0065] Insertion Pressure: 375 lbs

[0066] Hold Pressure: 100 lbs

[0067] Barrel and manifold temperatures 182° C.

[0068] Insert Nozzle Temperature 315° C.

[0069] Cycle Time: 11.4 seconds

[0070] The Average and Minimum Expected force required to pull the floss
out of the floss holder is shown on Table 2. The Minimum Expected value
for the pull out force was defined as the Average pull out force minus
three times the standard deviation. Sufficient Average and Minimum
Expected pull out force is considered by the makers of flossing devices
to be about 4 to more than five pounds.

[0071] Table 2 shows that both high twist, uncoated floss, and low twist,
coated floss met the Average pull out force requirements. For the low
twist, waxed floss, however, the Minimum Expected value of the pull-out
force is less than one pound.

[0072] In a following example, the Insert Nozzle temperature was reduced
from 315° C. to 255° C. to determine the effect of resin
temperature on pull out strength.

Example 3

[0073] The same mold and the same flosses were used as in Example 2. The
first floss was an unwaxed UHMWPE DSM SK 65 yarn with 3 twists per inch.
The second floss was UHMWPE DSM SK-65 400 denier, 1.5 twists per inch,
24.8 percent by weight of a coating composition containing 80 percent
microcrystalline wax and 20 percent Honeywell EVA PE400. The production
conditions were as follows:

[0080] Table 3 shows that both high twist, uncoated floss, and low twist,
coated floss made under the noted conditions met the minimum pull out
force requirements both for Average and Minimum Expected pull out force.

Example 4

[0081] Example 3 was repeated except that the Insert Nozzle temperature
was further reduced to 235° C. and then to 220° C. to
determine the effect of resin temperature on pull out strength. The
production conditions were as follows:

[0088] Table 4 shows that the low twist, coated floss made under the noted
conditions met both the Average and Minimum Expected pull out force
requirements.

Example 5

[0089] This experiment shows the affect of using a heat sink on the pull
out strength of single-use flossing devices. A mold was created similar
to the mold used in Example 1. One side of the mold included grooves that
were 0.800-inch wide and 0.002-inch deep, thus providing an aspect ratio
of 40:1. Heat sinks similar to those shown in FIG. 1 were machined into
the distal sections of the cavity in the other side of the mold halves
such that, when the halves were brought together, the heat sinks were
proximate the grooves and the length of floss positioned within the
groove. The floss used was the same as that of Example 4 (DSM 400, 1.5
twists per inch) and had applied thereto 25.7 percent of a coating
composition containing 80 percent microcrystalline wax and 20 percent
Honeywell EVA. A similar floss holder was made using a mold having a
groove with the same aspect ratio on one side, but without using a heat
sink on the other side.

[0097] Table 5 shows that by utilizing a heat sink proximate the groove
and the length of dental floss, the variation in the pull out force of
the floss holder made in such a mold is reduced significantly, as
evidenced by the reduction in the standard deviation by almost a factor
of 2. In addition, the Minimum Expected pull out force was about 5.6 lbs,
while the floss holder made in a mold without a heat sink was as low as
3.4 lbs. Thus, utilizing a heat sink in the lateral cavity portion of the
mold synergistically provides both a robust process of manufacture and a
floss holder with improved pull out, as evidenced by the reduction in
standard deviation and the significant increase in Minimum Expected pull
out force.

Example 6

[0098] Since temperature of the entering resin has been shown to affect
pullout force, experiments were conducted by changing the Insertion
Nozzle temperature. The same molds were used as in Example 5. The floss
used was the same as that of Example 4. The production conditions were as
follows:

[0105] Table 6 again demonstrates that utilization of a mold that includes
a heat sink in combination with a groove according to the present
invention synergistically reduces product and process variation and
significantly increases Minimum Expected pull out force at all injection
nozzle temperatures. For the particular floss and process conditions used
in this example, an insert nozzle temperature of about 220° C.
yielded the optimum results, e.g. a Minimum Expected pull out force of
about 7.3 lbs.

Example 7

[0106] The same molds were used as in Example 5. The floss used was DSM
400, 1.5 twists per inch with a 26.6 percent coating of microcrystalline
wax applied thereto. The production conditions were as follows:

[0113] Table 7 again demonstrates that utilization of a mold that includes
a heat sink in combination with a groove according to the present
invention synergistically reduces product and process variation and
increases Minimum Expected pull out force.

Example 8

[0114] Example 7 was repeated, but using highly twisted, uncoated floss.
The same molds were used as in Example 7. The floss used was DSM 400, 3
twist per inch with no wax coating applied thereto. The production
conditions were as follows:

[0121] Table 8 shows that utilizing a mold that includes a heat sink when
molding highly twisted, uncoated floss, actually reduces the Average and
Minimum Expected pull out force, while having little effect on the
variation (standard deviation) in the pull out force measurements. As
such, it has been surprisingly discovered that by using a heat sink in
the manufacture of single-use dental floss holders having wax coated
floss, improvements in both process and product are exhibited, which is
contrary to what one would expect.

Example 9

[0122] A consumer test was conducted comparing the flossing device with
the current floss (DSM 400 denier, Ultra High Molecular Weight
Polyethylene SK-65, 3-twists per inch with no coating), shown as
"Comparative" in Table 9, versus the same flossing device with a low
twist coated floss (DSM 400 denier, Ultra High Molecular Weight
Polyethylene SK-65, 1.5 twist per inch with a 26% coating of a
composition containing 80 percent microcrystalline wax and 20 percent
EVA, shown as "Invention" in Table 9.

TABLE-US-00009
TABLE 9
Average Consumer Rating of Products on a Scale of 1-10
(10 being highest) for a sample size (N) of 75.
Confidence
Attribute Invention Comparative Limits
Overall Liking 8.1 7.3 95%
Being easy to insert 8.4 7.7 95%
between teeth
Being easy to remove from 8.3 7.5 95%
between teeth
Not getting stuck between 8.2 7.4 90%
teeth
Being easy to slide 8.3 7.7 90%
between teeth
Being gentle on gums 8.7 7.9 90%
Cleaning well between 8.6 8.0 90%
teeth

[0123] The flossing device with the low twist wax coated floss was rated
significantly better (at a 95% confidence limit) in Overall Liking, Being
Easy to Insert between Teeth and Being Easy to Remove. The flossing
device with the low twist floss was considered better (at a 90%
confidence limit) on Not Getting Stuck between Teeth, Being Easy to Slide
between Teeth, Being Gentle on Gums and Cleaning Well Between Teeth. On
all other attributes, the products were rated equal, showing that that
the Inventive floss holder exhibited no disadvantages versus the
Comparative. This is significant in that it shows that flattening and
coating the floss provided additional preferred benefits, without
sacrificing any other properties, particularly with respect to fraying.